PMN Proeedings: 2011 Field Crops Rust Symposium

2011 Field Crops Rust Symposium:
Abstract

Mechanisms of Resistance to Rust Pathogens: Pre- and Posthaustorial.

Presenting Author: R. S. BRUEGGEMAN

Affiliation: Dept. of Plant Pathology, North Dakota State University, Fargo, ND, USA

The two best-characterized rust resistance mechanisms are represented by the host-pathogen interactions between the flax rust pathogen (Melampsora lini) and flax (Linum usitatissimum) and the wheat stem rust pathogen (Puccinia graminis) and barley (Hordeum vulgare). Characterization of the mechanisms determining pathogen recognition in these systems has identified common and contrasting themes regarding resistance components and the spatial-temporal detection of the pathogen. It has been demonstrated for flax rust resistance that AVR proteins are expressed and translocated from the haustoria into the plant cell, and a direct protein–protein interaction between the NBS-LRR resistance protein and the AVR protein determines detection. Flax rust resistance mechanisms follow Flor’s gene-for-gene model but resistance in barley is more complex. In contrast to flax, pathogen recognition in the barley Rpg1-mediated resistance mechanism occurs very early at the cell surface. Two distinct AVR proteins expressed in the spore are recognized, followed by phosphorylation of the protein kinase domain of RPG1 within minutes of spore contact with the leaf surface. Our research has also determined that the rpg4-mediated stem rust resistance in barley requires the interaction of four genes at the complex rpg4/Rpg5 locus and two contain the typical NBS-LRR protein domains. Dominant NBS-LRR resistance genes mediate the rpg4 resistance, but a protein phosphatase appears to act as a dominant susceptibility factor contributing the recessive nature of this complex resistance locus. Although common components mediate resistance in both flax and barley, it appears that barley rust resistance has several deviations from the typical gene-for-gene model.